Retractable dental syringe

Abstract

A single use retractable medical device dispenses fluids from a separable carpule. A retraction mechanism having a spring loaded needle holder with a double ended needle is mounted in the front of a housing by means of a push ring (separable member) slidingly mounted on a widened portion of the needle holder. An outer edge of the push ring grips or is restrained by the inner wall surface of the housing to hold the needle holder in place. A carpule positioned through an opening in back of the housing is operated by a plunger which drives a separable two-part piston to unload medicine from the carpule through the needle. At the end of an injection, the plunger is depressed further. The carpule moves forward to remove the push ring thereby freeing the needle holder for retraction into the carpule through the front opening of the carpule. As the needle is retracted into the housing from one end, the edge of the thumb cap of the plunger disappears into an opening at the opposite end of the housing. The back of the housing may have the traditional thumb ring or it may have a “disappearing” thumb cap which is received into a widened opening in the back of the housing to thwart removal.

What is claimed:  
     
       1. A retractable dental syringe, comprising: 
       a carpule having a fluid chamber and a front seal and a rear seal for holding fluid in the chamber;  
       a tubular housing which accepts the carpule, the tubular housing having a front end portion holding a retractably mounted needle in fluid communication with the fluid chamber for dispensing fluid contents of the carpule;  
       a depressible plunger which presses against the rear seal to dispense fluid from the carpule; and  
       the carpule being adapted to release and receive the retractably mounted needle once the fluid id dispensed as the plunger and the carpule are moving forward in response to depression of the plunger.  
     
     
       2. The dental syringe of claim  1  wherein the tubular housing has an open side through which the carpule is accepted. 
     
     
       3. The dental syringe of claim  1  wherein the needle is retractably mounted by means of a ring member in combination with a needle holder. 
     
     
       4. The dental syringe of claim  3  wherein moving the carpule releases and receives the needle by moving the ring member and relatively moving the front seal thereby freeing the needle holder to pass into the fluid chamber of the carpule. 
     
     
       5. The dental syringe of claim  3  whereby the needle holder is mounted in the front of the tubular housing and whereby movement of the carpule in response to the plunger causes the front seal to be dislodged by the needle holder thereby creating an open space so that the needle holder can retract the needle into the carpule. 
     
     
       6. The dental syringe of claim  1  wherein the carpule has a mouth which is adapted to release and receive the retractably mounted needle once the fluid is dispensed in response to further depression of the plunger. 
     
     
       7. The dental syringe of claim  6  wherein the tubular housing and depressible plunger are provided with catches to keep the plunger in the housing after the needle is retracted into the carpule. 
     
     
       8. The dental syringe of claim  6  wherein the carpule has a tubular wall which defines the fluid chamber and the depressible plunger has a front portion comprising an elongated tubular wall portion which slides in proximity to the wall of the carpule inside the carpule. 
     
     
       9. The dental syringe of claim  1  wherein the rear seal comprises a slidable separable two-part seal comprising a core part and a rim part and wherein the depressible plunger presses against the rim part. 
     
     
       10. The dental syringe of claim  9  wherein the syringe is emptied by depressing the plunger until the two-part seal is moved to the front end portion of the tubular housing and whereupon further depression of the plunger moves the carpule in a direction towards the needle without moving the core part of the two-part seal whereby an opening is created for retraction of the needle into the carpule. 
     
     
       11. A retractable dental syringe, comprising: 
       a tubular housing adapted to accept a carpule, the tubular housing having a front portion, an intermediate portion and a rear portion;  
       a carpule having a fluid chamber, a front seal and a rear seal for enclosing fluid in the chamber, the carpule having a mouth in front and being sized to fit said housing;  
       a depressible plunger which empties the carpule by moving the rear seal forward to an end-of-injection position;  
       needle structure in fluid communication with the carpule, the needle structure being retractably mounted in the front of the housing for retraction into the carpule;  
       whereby the mouth of the carpule is adapted to release the retractable needle for retraction into the carpule in response to depression of the plunger beyond the end-of-injection position of the plunger.  
     
     
       12. The dental syringe of claim  11  wherein the carpule is positionable for use in the intermediate portion of the tubular housing. 
     
     
       13. The dental syringe of claim  12  wherein the carpule is sized to substantially occupy the intermediate portion of the housing. 
     
     
       14. The dental syringe of claim  13  wherein cooperating catches are provided on the housing and the depressible plunger to keep the plunger in the housing after the plunger reaches the end-of-injection position. 
     
     
       15. The dental syringe of claim  11  wherein the carpule has a tubular wall which forms the fluid chamber and wherein the depressible plunger has a front portion comprising an elongated tubular wall portion which slides in proximity to the wall of the fluid chamber inside the carpule. 
     
     
       16. The dental syringe of claim  15  wherein the carpule may be installed and removed through the side of the housing. 
     
     
       17. The dental syringe of claim  11  wherein the needle structure comprises a hard part which holds a needle and a releasable part which holds the hard part in position. 
     
     
       18. The dental syringe of claim  17  wherein the mouth of the carpule moves the releasable part forward after the end-of-injection position is reached during continued depression of the plunger. 
     
     
       19. The dental syringe of claim  18  wherein the releasable part that is moved by the mouth of the carpule comprises an “O” ring. 
     
     
       20. The dental syringe of claim  18  wherein the releasable part comprises a ring member which frictionally engages the hard part of the needle structure along a substantial common interface. 
     
     
       21. A method of operating a syringe, comprising: 
       providing an elongated tubular housing having a front portion containing a retractable needle structure having a retractable needle holding part and a separable part which releases the needle holding part and needle for retraction;  
       providing a carpule for the tubular housing, the carpule having a mouth in front with a front seal and a back portion with a slidable and separable two-part seal, the carpule having a fluid chamber between said seals in fluid communication with the needle;  
       providing a depressible plunger having a tubular front portion in pressing contact with one part of the separable two-part seal;  
       depressing the plunger to move the two-part seal forward to a sufficient extent as to expel substantially all fluid from the fluid chamber through the needle; and  
       moving the carpule toward the needle structure in response to additional depression of the plunger to thereby automatically retract the needle holding part into the carpule through the mouth of the carpule.  
     
     
       22. The method of claim  21 , wherein the step of moving the carpule toward the needle structure is accompanied by the steps of: 
       moving the separable part relative to the needle holding part, and moving one part of the separable two-part seal relative to the other part of said seal.  
     
     
       23. The method of claim  22  wherein the step of moving the carpule toward the needle structure includes the step of moving the front seal from the mouth of the carpule in a direction away from the needle holding structure. 
     
     
       24. The method of claim  21  wherein: 
       the step of providing a needle holding structure includes the step of providing a separable part comprising a ring member; and  
       the step of automatically retracting the needle holding part into the carpule includes the step of separating the ring member from the needle holding part.  
     
     
       25. The method of claim  23  wherein the step of moving the front seal out of the mouth of the carpule includes the step of moving the front seal relative to said other part of the separable two-part seal in a direction away from the needle holding structure.